auxiliary devices for load-lifting machines. They are used to pick up and hold the load during various moving and loading operations. Hooks, augmented by other devices when necessary, are used for direct pickup of the load.
Load-gripping devices must be convenient and safe in operation, they must ensure the safety of the freight and be as light as possible, and they must grasp and release the load quickly. The choice of a device depends on the properties, size, form, and weight of the load to be moved, as well as the characteristics of the industrial process involved. Depending on the type of freight, the devices are classified into groups used for piece goods and for bulk or liquid goods and, depending on the type of drive, into manual and automatic types (so-called avtostropy, literally “automatic cargo slings”).
The devices that are the simplest in design are the so-called slings, which are used for piece goods. They may be sections of cable or welded link chains whose ends are welded together or are equipped with eyelets (special metal rings), hooks, or shackles. Quick-action claw grips and cam gripping devices are widely used for lifting boxes, kegs, sacks, and rolled sheet steel. Bulk goods are picked up and moved by buckets, dippers, and clamshells; liquids are picked up and moved by buckets and scoops.
Avtostropy make it possible to free large numbers of laborers for other work, provide safer working conditions, and reduce labor intensity. They are used for reinforced-concrete structural members, containers, and packaged loads. Freight electromagnets are widely used for the automatic pickup of ferrous metal loads. Several electromagnets suspended from a single crossbeam are used to lift long loads. Vacuum load-gripping devices with grips, heads, or flexible suction disks are used for lifting loads with smooth flat surfaces (sheets, building assemblies, or boxes). The principle of operation of these suction disks is based on the differential between atmospheric pressure and the pressure inside the disk.
The improvement of modern load-gripping devices is proceeding both along the lines of development of new designs for automatic grips and the creation of specialized grips for particular loads—for example, rolls of sheet steel, packages of sheet material, containers, and logs.
A. A. PAWCHOMENKO